This invention relates to a process for the preparation of polyalkenamers by the ring-opening polymerization of cyclic olefins employing a catalyst containing a metal of Subgroups 5 through 7 of the periodic table or a compound thereof and to novel polyalkenamers thus-produced.
It is known that cyclic olefins containing at least one substituted ring double bond can be polymerized under ring-opening conditions. The catalysts employed for this ring-opening polymerization are supported catalysts which contain a metal of Subgroups 5 through 7 of the periodic table, or the compounds thereof. See German published application DAS No. 1,072,811. Preferred catalysts are the reaction products of compounds of the above-mentioned metals with organometallic compounds or hydrides of metals of Main Groups 1 through 3 or Subgroup 2 of the periodic table, as well as optionally compounds which contain one or more hydroxy and/or sulfhydryl groups. See French Pat. Nos. 1,394,380 and 1,467,720; the published disclosures of Dutch patent application Ser. Nos. 65-10,331; 66-05,105; 66-14,413; 67-04,424; 68-06,208; and 68-06,211. The catalysts described therein contain compounds of molybdenum or tungsten and, as organometallic compounds, usually organoaluminum compounds. According to the published texts of Dutch patent applications Ser. Nos. 67-14,559 and 68-06,209, vanadium, niobium, tantalum, rhenium, technetium, or manganese can also be components of such catalyst systems.
In accordance with German unexamined published application DOS No. 1,909,226, it is also possible to employ catalyst systems containing a halide or an oxyhalide of molybdenum or tungsten wherein the stage of oxidation of the metal is 4, 5 or 6, an aluminum trihalide.
With the aid of these catalysts, a great variety of polymers can be prepared with structures which are strictly regular along the polymer chains, the structure of the polymer units being exclusively dependent on the cycloolefin employed as the monomer. Thus, it is possible, for example, to produce linear polymers by the polymerization of monocyclic olefins; polymers having recurring polymer units containing a single ring by the polymerization of bicyclic olefins; and, in general, polymers having recurring polymer units which contain one ring less than the starting monomer by the polymerization of polycyclic olefins.
The polyalkenamers produced by the polymerization of monocyclic olefins are of particular interest for the additional reason that, depending on the cycloolefin employed, it is possible to prepare polymers having differing double bond content. Thus, polybutenamers which are free of vinyl groups, i.e., pure 1,4-polybutadienes, are obtained from cyclobutene, 1,5-cyclooctadiene, and 1,5,9-cyclododecatriene. Polypentenamers are obtained from cyclopentene which have three --CH.sub.2 -groups disposed between the double bonds. Polyoctenamers are produced from cyclooctene which correspond to a completely regular semi-hydrogenated 1,4-polybutadiene. Polydodecenamers are prepared from cyclododecene corresponding to a two-thirds hydrogenated 1,4-polybutadiene in which remaining double bonds are arranged in the molecule at regular intervals. Accordingly, it is possible to produce polymers, the structures of which represent variations from pure 1,4-polybutadienes, free of vinyl groups, to strictly linear polyethylenes or polymethylenes.
It is likewise known that the average molecular weight or the degree of polymerization of a polymer affects properties of the polymer and thus its usefulness in any particular field of application, as well as its characteristics during the production and processing. Thus, polymer solutions of equal weight concentration of polymer are more viscous, the higher the molecular weight of the polymer in solution. Thus, difficulties are encountered with solutions of very high-molecular polymers, e.g., during the polymerization, for example, in the mixing or obtaining satisfactory heat exchange, and increased energy requirements for the agitating step result. Also, the further processing of very high-molecular polymers is difficult. For this reason, they are often degradated mechanically, chemically, or thermally prior to the final shaping procedure, eg., injection-molding, extrusion, or calendering.
The polyalkenamers obtained during the ring-opening polymerization of cycloolefins are normally very high-molecular. Because of the above-described difficulties with polymers of very high molecular weight, attempts have been made in the prior art to develop processes for regulating the molecular weight of the polymers producible by a great variety of polymerization methods. In the polymerization of .alpha.-olefins with organometallic mixed catalysts, the so-called hydrogen regulation, i.e., polymerization in the presence of a certain partial hydrogen pressure, proved useful. Other possibilites for controlling the molecular weight of .alpha.-olefin polymers were varying the catalyst components, elevating the temperature or adding alkylzinc or alkylcadmium compounds during the polymerization.
Although organometallic mixed catalysts or related catalyst systems are also employed in the ring-opening polymerization of cycloolefins, the methods for molecular weight regulation employed in the polymerization of the .alpha.-olefins either are unsuccessful or exhibit definite disadvantages which made the use of such methods difficult, if not impossible. Thus, hydrogen, for example, up to an excess pressure of 4 atmospheres exerts practically no influence at all on the molecular weight of the polyalkenamers prepared by the ring-opening polymerization of cycloolefins. Even if hydrogen were effective at pressures higher than those mentioned above, the hydrogen regulating method would require increased investment costs, since the plant would have to be designed for pressures which do not occur in the unregulated ring-opening polymerization of the cycloolefins which, under normal pressure, are present in the liquid phase or in solution at the polymerization temperature. Although the molecular weight of the polyalkenamers can be reduced by employing a higher polymerization temperature, the yield and the steric uniformity of the polymers are impaired in so doing. Moreover, due to the temperature sensitivity of the mixed catalysts customarily employed for the ring-opening polymerization of cycloolefins, such catalysts become inactive above 40.degree.-50.degree. C. in a short period. Also, modifications of an optimal catalyst system can strongly impair yield. See, for example, Dutch patent application Ser. No. 66-05,105, p. 16.
The last of the above-mentioned methods for controlling the molecular weight during the polymerization of .alpha.-olefins with organometallic mixed catalysts, i.e., using an alkylzinc or alkylcadmium compound as the controlling agent, is of little practical use, even if it were effective in the ring-opening polymerization of cycloolefins, because such zinc and cadmium compounds are very toxic and can be prepared only with difficulty and thus are expensive.
The only process heretofore known wherein polymers are obtained which exhibit improved processability is described in British patent No. 1,098,340. In this process, cyclic monoolefins are copolymerized under ring-opening in the presence of a conjugated diolefin, such as, for example, butadiene, isoprene, or 1,3-pentadiene. The thus-produced copolymers contain polymer units derived from both the cycloolefin and the conjugated diolefin, in varying molar ratios.
As shown in Comparative Experiments N through T in Table 3, conjugated dienes, although they influence the molecular weight of the polyalkenamers produced in polymerizations conducted in their presence, also are more or less strong catalyst poisons. Thus, for example, the presence of only 1 mol% of 1,3-butadiene, 5 mol% of isoprene, 5 mol% of 2,3-dimethyl-1,3-butadiene, or 10 mol% of 2,4-hexadiene, results in the complete inhibition of the polymerization catalyst and no polymer is obtained. Cyclic conjugated diolefins also cause a pronounced lowering of the yield of polymer. Moreover, it is not possible using such dienes as polymerization regulators to produce polymers which are waxy or oil-like products having very low molecular weights, e.g., about 500-5000.
In our prior filed U.S. application Ser. No. 70,497 filed Sept. 8, 1970, now U.S. Pat. No. 3,816,382, we claim a process for the regulation of molecular weight of polyalkenamers by the addition of monoolefins, preferably .alpha.-olefins, during the polymerization. The molecular weight of polyalkenamers can be regulated with a very high degree of success by this process. However, there is a great interest in polymers having functional terminal groups, which can be employed for further reactions, such as, for example, cross-linking reactions or for the construction of other defined polymer structures, e.g., block copolymers or stellate polymers. For example, a stellate structure is obtained by the reaction of a unilaterally lithium-terminated polymer, e.g., a polybutadiene or polystyrene produced in a polymerization which employs butyllithium as the catalyst, with a tri- or tetrahalogen compound, such as, for example, methyltrichlorosilane, silicon tetrachloride, or carbon tetrabromide. A chain of polymer terminating at both ends in halogen can be reacted with a unilaterally metal-terminated chain of another polymer to form block copolymers. Polymer chains terminating in hydroxyl groups can be cross-linked with di-, tri-, or polyisocyanates or other polyfunctional compounds, such as, for example, acid chlorides of polybasic acids. These examples are typical but not complete and merely illustrate that such reactions of "telechelic polymers" (U.S. Pat. No. 3,244,664) have gained increasing importance in recent times. Functional end groups also often influence the practical application properties of the polymers and effect, for example, an improved adhesion to surfaces and/or an improved compatibility with other polymers. Thus, there is an increasing need for processes yielding polymers having defined functional end groups.
Accordingly, it is an object of the present invention to provide a process which makes possible, in a simple manner, to simultaneously regulate the molecular weight of polyalkenamers produced by the ring-opening polymerization of cyclic olefins and to introduce functional terminal groups into the polymer molecule. Another object is to provide novel polymers thus-produced. Other objects will be apparent to those skilled in the art to which this invention pertains.